Deposited Si photodetectors for silicon nitride waveguide based optical interposer

ABSTRACT

Embodiments herein describe optical interposers that utilize waveguides to detect light. For example, in one embodiment, an apparatus is provided that includes an optical detector having a first layer. The first layer includes at least one of polysilicon or amorphous silicon. The first layer forms a diode that includes a p-doped region and an n-doped region. The apparatus further includes a waveguide optically coupled to the diode and disposed on a different layer than the first layer.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to opticalinterposers and more specifically, to optical interposers that usewaveguides formed from silicon and nitride to detect light in a dopedpolysilicon or amorphous silicon layer.

BACKGROUND

Fiber optic components are used in a wide variety of applications as amedium for transmission of digital data (including voice, internet andIP video data). Fiber optics is becoming increasingly more common due tohigh reliability and large bandwidths available with opticaltransmission systems. Interposers can function as substrates foroptical, opto-electrical, and electrical components and provideinterconnections to optically and/or electrically interconnect theoptical/opto-electrical/electrical components. To measure an opticalsignal, a tap coupler is inserted near a waveguide to redirect a fewpercent of the optical energy from the waveguide into a separate opticalport.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments.

FIG. 1 illustrates an interposer that includes an optical detector,according to one embodiment disclosed herein.

FIG. 2A illustrates a cross-sectional view of the optical detectordepicted in FIG. 1, according to one embodiment disclosed herein.

FIG. 2B illustrates a cross-sectional view of an optical detector,according to one embodiment disclosed herein.

FIG. 3A illustrates a simulation of an optical signal traveling througha waveguide, according to one embodiment disclosed herein.

FIG. 3B illustrates a simulation of an optical signal traveling througha waveguide, according to one embodiment disclosed herein.

FIG. 3C illustrates a simulation of an optical signal traveling througha waveguide, according to one embodiment disclosed herein.

FIG. 4 illustrates an example graph that plots radiation received by apolysilicon layer for a waveguide having various widths.

FIG. 5 illustrates one view of an optical detector, according to oneembodiment disclosed herein.

FIG. 6 illustrates one view of an optical detector, according to oneembodiment disclosed herein.

FIG. 7 illustrates a method of operation, according to one embodimentdisclosed herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Overview

One embodiment presented in this disclosure is an apparatus thatincludes an optical detector having a first layer. The first layerincludes at least one of polysilicon or amorphous silicon. The firstlayer forms a diode that includes a p-doped region and an n-dopedregion. The apparatus further includes a waveguide optically coupled tothe diode and disposed on a different layer than the first layer. Invarious embodiments, the waveguide is silicon nitride, siliconoxy-nitride, or a polymer.

In another embodiment, a method of operating an apparatus is providedthat includes transmitting an optical signal through a waveguide thatcauses a corresponding electrical signal in an optically coupled firstlayer that has been doped to have a diode. The waveguide is on adifferent layer than the first layer and includes silicon and nitride.Thereafter, the method measures the corresponding electrical signal.

In yet another embodiment, an interposer is provided that includes anoptical detector that includes a first layer that forms a diode. Theinterposer also includes a waveguide optically coupled to the diode anddisposed on a different layer than the first layer. The waveguide ismade of a material that includes one of silicon nitride or siliconoxy-nitride.

EXAMPLE EMBODIMENTS

Embodiments herein describe optical interposers that include opticaldetectors optically coupled to waveguides formed from silicon andnitride. In one embodiment, the optical interposer is an interface byreceiving an optical signal and rerouting the optical signal to adifferent connection. The optical interface can convert the receivedoptical signal into a corresponding electrical signal. In someembodiments the waveguides are made of silicon nitride. In otherembodiments, the waveguides are made of silicon oxy-nitride. “Siliconnitride” and “silicon oxy-nitride” are used interchangeably in thisdocument. One of the advantages of using silicon nitride or siliconoxy-nitride rather than silicon in the waveguides is that interposersbased on these materials are less expensive. In addition, theinterposers disclosed herein do not require an SOI or germanium (“Ge”)layer and do not require the use of a separate “tap detector” to monitorlight in the photodetector.

“Taper” as used herein is defined as diminishing or reducingdimension(s) of the waveguides described herein. The “near IR frequencyrange” is defined herein as relating to electromagnetic radiation havingwavelengths between about 0.7 and 3.0 microns. “Responsivity” as usedherein is defined as the electrical current output per the optical inputof the photodetector.

FIG. 1 illustrates an interposer 100 that includes an optical detector102, according to one embodiment disclosed herein. The optical detector102 receives an optical signal from an optical waveguide 106. Theoptical detector 102 also includes electrical contacts 104 ₁ and 104 ₂(collectively “electrical contacts 104”). The optical detector 102converts the optical signal, received via the optical waveguide 106,into an electrical signal (e.g., a voltage or current) and transmits theelectrical signal via electrical contacts 104 to electrical components(not shown). For example, the electrical contacts 104 can becoupled/connected to an electrical integrated chip (“IC”). The opticaldetector 102 can also receive electrical signals via the electricalcontacts 104. For illustrative purposes only, the diodes have beendescribed herein as “p-i-n diodes.” However, other embodiments may use apn diode that lacks an intrinsic area.

Silicon-nitride based optical interposers are increasingly used tosimplify packaging, to reduce cost, and turn-around time. For example, asilicon-nitride interposer may not require a SOI or germanium (“Ge”)layer which can reduce turn-around time. Integrated detectors are usedfor implementing control loops in silicon based photonic interposers, inorder to facilitate fiber alignment, laser burn-in, and optical powerlevel monitors, etc. The high concentration of defects (crystallinegrain boundaries) inherent to polysilicon and amorphous silicon givesrise to defect states, which act as absorbers of light in thenear-infrared wavelength range.

The optical detectors (e.g., optical detectors 102 and 103) can beimplemented in “end-of-line” configuration using tap couplers or in anin-line configuration. One of the advantages of the “in-line” detectorconfiguration is that it does not “tap” some percentage of the opticalenergy into a separate optical port and does not rely on adding anoptical tap into the waveguide 106 it is monitoring. This minimizes bothoptical loss, and implementation complexity.

FIG. 2A illustrates a cross-sectional view of the optical detector 102depicted in FIG. 1, according to one embodiment disclosed herein. InFIG. 2A, a first layer 200 that contains polysilicon or amorphoussilicon has been doped to form a p-i-n diode that includes an n-dopedregion 204, a p-doped region 206 and an intrinsic region 208. Lighttransmitted in the waveguide 106 interacts with the intrinsic region208. The high density of sub-band states in the first layer 200 leads tothe creation of free charges in a concentration proportional to thelight intensity. The p-i-n doping profile sweeps these charges to thecontacts 104, where they can be extracted and sensed. In one embodiment,properties of the first layer 200 can be optimized for light detectionutilizing annealing techniques used in polysilicon and amorphous silicondisplay fabrication technologies.

The first layer 200 includes two surfaces. One of those surfaces (alsoreferred to herein as a “first surface”) is connected to the electricalcontacts 104. The first layer 200 also includes another surface (alsoreferred to herein as a “second surface”) that opposite is to the firstsurface and is substantially parallel to the first surface. Thewaveguide 106 is positioned in a facing relationship with the secondsurface of the first layer 200. The dimensions of the waveguide 106 aresuch that it has a single mode. For example, the waveguide 106 mayinclude a thickness 210 of about 100 nm to about 500 nm and a width 212of about 400 nm to about 4000 nm. Although the thickness 210 and thewidth 212 can be tapered, for illustrative purposes only examples areprovided herein that taper the width 212 of the waveguide 106. The firstand second surfaces of the first layer 200 are in contact with at leastone layer of material 214 that has a different refractive index thaneither the polysilicon or the material composing the waveguide 106.Moreover, the material 214 surrounds the waveguide 106. In oneembodiment, the material 214 is silicon dioxide. When an optical signalpasses through the waveguide 106 some light radiates through thematerial 214 and into the first layer 200 causing an excitation ofelectrons in the intrinsic region 208. This generates an electric signalthat can be measured to determine the intensity of the light passingthrough the waveguide 106. The distance between the waveguide 106 andthe first surface of the first layer 200 may be about 0.2 microns toabout 2.2 microns. FIGS. 2A and 2B are cross sectional views of thewaveguide 106 and first layer 200 extends in direction into and out ofthe page.

FIG. 2B illustrates a cross-sectional view of an optical detector 103,according to one embodiment disclosed herein. The optical detector 103depicted in FIG. 2B operates similarly to the optical detector 102depicted in FIG. 2A. However, in FIG. 2B the waveguide 106 is depositedbefore the first layer positioned facing the second surface of the firstlayer 200. When light travels through the waveguide 106 energy isradiate through the material 214 and onto the second surface of thefirst layer 200. The distance between the waveguide 106 and the secondsurface of the first layer 200 may be about 0.2 microns to about 2.2microns.

In one embodiment, the first layer 200 is formed by depositing a layerof polysilicon or amorphous silicon about 100-200 nm above or below thewaveguide. In one embodiment, the first layer 200 is thermally annealedto partially crystallize the first layer 200. The first layer 200 isdoped with n- and p-dopants to form diode structure. Contacts are alsoformed to the doped n and p regions as shown in FIG. 2. Lithographicpatterning and etching of the first layer 200 is performed. An uppercladding layer is deposited to protect the first layer 200, contacts,and waveguide 106. Metal electrical contacts are formed for connectionwith external components.

FIGS. 3A, 3B, and 3C depict simulations of an optical signal through awaveguide where each of the waveguides has different dimensions than theother waveguides depicted. Shading is used in FIGS. 3A, 3B and 3C toindicate the intensity of the optical signal is the greatest near thecenter of the waveguide. These figures also show that a silicon nitridewaveguide that is wider and/or thicker will confine more light withinthe waveguide and provide radiation of less light to the polysiliconlayer.

Changing the dimensions of the waveguide provides one way to tune thesensitivity of the detector 102 and how much energy the first layer 200receives from the waveguide 106. In addition to changing the dimensionsof the waveguide 106, the distance between the waveguide 106 and thefirst layer 200 can be changed to tune the sensitivity of the detector102 and how much energy the detector 102 receives from the waveguide106. For example, increasing the distance between the waveguide 106 andthe first layer 200 reduces the sensitivity of the detector 102.

The sensitivity of the detector 102 can also be tuned by changing thelocation(s) of the dopant(s) on the first layer 200. For example, FIGS.2A and 2B depicts the n-doped region on the left side of the first layer200 and the p-doped region on the right side of the first layer 200. Inone embodiment, the n-doped region can be moved further to the left sideof the first layer 200 and/or the p-doped region and moved further tothe right side of the first layer 200 to reduce thesensitivity/efficiency of the detector 102. In one embodiment, thelocation(s) of the dopants can be changed, the dimensions of thewaveguide 106 can be changed, and/or the distance between the waveguide106 and the first layer 200 can be changed to tune the detector 102.Further, the distance between the electrical contacts 104 can be movedeither further apart or closer together to tune sensitivity. Forexample, the distance between the electrical contacts 104 can be about 2microns to about 400 microns. The distance between the electricalcontacts 104 may be kept far enough away from each other to avoidinteracting with the optical field.

FIG. 3A depicts a simulation 300 that includes a silicon nitridewaveguide 302 having a width of about 350 nm. The distance between thewaveguide 106 and the first surface of the first layer 200 may be about0.2 microns to about 2.2 microns. The shading in the simulation 300illustrates that some of the optical signal has traveled outside (i.e.,is not restricted within the waveguide 302) of the waveguide 302. Someof the energy from the optical signal that is outside of the waveguide302 is detected and converted into an electrical signal by the firstlayer 301.

FIG. 3B depicts a simulation 304 that includes a waveguide 306. Thewaveguide 306 has a width of abut 500 nm and is greater than the widthof waveguide 302. The simulation 304 shows that when compared to thesimulation 300, more of the optical signal is within waveguide 306 thanin the waveguide 302, and as a result, there is less energy from theoptical signal that is outside of the waveguide 306 and available fordetection by the first layer 305 than on the outside of the waveguide302 and available to the first layer 301.

Likewise, FIG. 3C depicts a simulation 308 where waveguide 310 has awidth of about 1000 nm and is wider than the waveguides 302 and 306. Thewaveguide 310 has more of the optical signal restricted to the waveguide310 and less of the optical signal radiates towards the first layer 309than towards first layer 301 and first layer 305. In short, increasingthe width of the waveguide means that less of that optical signalradiates outside of the waveguide and towards the first layer. FIGS. 3A,3B and 3C show that by changing the dimensions (i.e., the thickness 210and/or the width 212) of the waveguide a different amount of lightinteracts with the first layer.

FIG. 4 illustrates an example of a graph 400 that includes a plot 402 ofradiation received by a first layer for a waveguide having variouswidths. For the graph 400, the first layer 200 has a width of about 120nm. As shown by the X-axis, a range of about 500 nm to about 2000 nm isused as the width of the waveguide 106 to acquire plot 402. Plot 402shows that as the width of the waveguide 106 increases the percentage ofthe optical signal that is received by the first layer 200 is reduced.

FIG. 5 illustrates a top or bottom view of an optical detector 500relative to the cross sectional views shown in FIGS. 2A and 2B,according to one embodiment disclosed herein. The waveguide 106 in FIG.5 includes a portion 501 that is optically coupled to the first layer200. In some embodiments, portion 501 has a length of about 100 micronsto about 200 microns. Illustratively, the waveguide 106 is facing theintrinsic region 208 of the first layer 200. The portion 501 includesseveral subsections having different dimensions. For example, portion501 includes subsections 502, 504 and 506. Subsection 502 is tapered sothat the width dimension is smaller than before subsection 502. Forexample, the width of subsection 502 is tapered towards subsection 504.Subsection 504 proceeds from subsection 502 for a length “L” towardssubsection 506. In this example, the width of the waveguide 106 in thesubsection 504 is substantially constant. At subsection 506, the widthof the waveguide 106 is increased until the width of the waveguide 106is similar to the dimensions of the waveguide before subsection 502.Tapering the width at subsection 502 may cause more of the opticalsignal to radiate outside of the waveguide and into the intrinsic region208 of the optical detector 500. As such, the subsections 502, 504 and506 can increase the responsivity of the optical detector 500 relativeto a waveguide that extends below the optical detector 500 withouttapering.

FIG. 6 illustrates a top or bottom view of an optical detector 600relative to the cross sectional views shown in FIGS. 2A and 2B,according to one embodiment disclosed herein. In FIG. 6, the waveguide106 has a first portion 604 that tapers for a length 602 to one end andterminates underneath (or above) the first layer 200 (more specifically,the waveguide 106 terminates underneath (or above) the intrinsic region208). The first portion 604 is disposed on a plane that is parallel tothe first layer 200 (i.e., the diode). That is, the waveguide 106 doesnot extend beyond the two opposite ends of the detector 600. In thisembodiment, tapering the waveguide 106 until it terminates may transmitmore of the optical signal into the first layer 200 when compared to theoptical detector 500 shown in FIG. 5. As examples, the optical detector600 may be used to help with optical alignment and/or after a tapcoupler. In one embodiment, the width 212 of the waveguide 106 is about400 nm to about 4000 nm tapers at one end from about 0 to about 500 nm.

FIG. 8 illustrates a method 800 of operating an optical detector,according to one embodiment disclosed herein. The method 800 includesblock 802 where an optical signal is transmitted through an opticalwaveguide 106 that is made of materials that include silicon and nitride(e.g., silicon nitride and silicon oxy-nitride). The waveguide 106 isoptically coupled to a first layer 200. The first layer 200 is doped toform either a pn diode or a p-i-n diode. As the optical signal passesthrough the waveguide 106 some of that signal is received in the firstlayer 200. At block 804, the light received by the first layer 200causes a corresponding electrical signal in the diode 102 that ismeasured.

In the preceding, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thedescribed features and elements, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the preceding aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s).

As will be appreciated by one skilled in the art, the embodimentsdisclosed herein may be embodied as a system, method or computer programproduct. Accordingly, aspects may take the form of an entirely hardwareembodiment, an entirely software embodiment (including firmware,resident software, micro-code, etc.) or an embodiment combining softwareand hardware aspects that may all generally be referred to herein as a“circuit,” “module” or “system.” Furthermore, aspects may take the formof a computer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality and operation of possible implementations ofsystems, methods and computer program products according to variousembodiments. In this regard, each block in the flowchart or blockdiagrams may represent a module, segment or portion of code, whichcomprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block may occurout of the order noted in the figures. For example, two blocks shown insuccession may, in fact, be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts, or combinations of special purpose hardware andcomputer instructions.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. Apparatus comprising: an optical detector comprising adetection layer consisting of a doped material selected from a groupconsisting of doped polysilicon and doped amorphous silicon, wherein thedoped material forms a diode, wherein the diode comprises a p-dopedregion and an n-doped region, wherein the detection layer comprises afirst refractive index; a waveguide optically coupled to the diode anddisposed on a different layer than the detection layer, wherein thewaveguide comprises a second refractive index; and a material layerdisposed between the detection layer and the waveguide, wherein thematerial layer comprises a third refractive index, wherein the thirdrefractive index is different than the first refractive index and thesecond refractive index, wherein a portion of light energy traveling viathe waveguide radiates through the material layer to the opticaldetector.
 2. The apparatus of claim 1 wherein the waveguide is formedfrom one of silicon, silicon nitride, silicon oxy-nitride, amorphoussilicon, a polymer, and polysilicon.
 3. The apparatus of claim 1 whereinthe n-doped region is disposed on a first end of the detection layer andthe p-doped region is disposed on a second, opposite end of thedetection layer.
 4. The apparatus of claim 1 wherein the detection layercomprises: a first surface; a first electrical contact contacts thefirst surface in the p-doped region; and a second electrical contactcontacts the first surface in the n-doped region, wherein the waveguideis in a facing relationship with the first surface and is disposedbetween the first electrical contact and the second electrical contact.5. The apparatus of claim 1 wherein the detection layer comprises anintrinsic region disposed between the n-doped and p-doped regions diode,wherein the waveguide is disposed on an axis that extends through theintrinsic region and is perpendicular to the detection layer.
 6. Theapparatus of claim 5 wherein the detection layer comprises: a firstsurface; and a second surface that is opposite to the first surface,wherein a first electrical contact contacts the first surface in thep-doped region and a second electrical contact contacts the firstsurface in the n-doped region, and wherein the waveguide is in a facingrelationship with a portion of the second surface that includes theintrinsic region.
 7. The apparatus of claim 1 wherein the detectionlayer comprises: a first surface; and a second surface that is oppositeto the first surface, wherein a first electrical contact contacts to thefirst surface in the p-doped region and a second electrical contactcontacts the first surface in the n-doped region, and wherein thewaveguide is in a facing relationship with the second surface.
 8. Theapparatus of claim 1 wherein the waveguide includes a first portion thatis adapted to transmit an optical signal to the diode, the first portioncomprising at least one dimension that tapers along a direction that issubstantially parallel to the detection layer, wherein the waveguideterminates at an end of the first portion, wherein the end of the firstportion is disposed on a plane that intersects the diode.
 9. Theapparatus of claim 1 wherein the waveguide includes a first portion thatis adapted to transmit an optical signal to the diode, the first portionincludes at least one dimension that tapers until reaching a secondportion of the waveguide that does not taper, wherein the waveguidecomprises a third portion connected to the second portion, wherein thethird portion has a reverse taper relative to the first portion.
 10. Aninterposer comprising: an optical detector comprising a detection layerconsisting of a first doped material selected from a group consisting ofdoped polysilicon and doped amorphous silicon, wherein the first dopedmaterial forms a diode, wherein the detection layer comprises a firstrefractive index; a waveguide optically coupled to the diode anddisposed on a different layer than the detection layer, the waveguide ismade of a second material that comprises one of silicon nitride andsilicon oxy-nitride, wherein the waveguide comprises a second refractiveindex; and a material layer disposed between the detection layer and thewaveguide, wherein the material layer comprises a third refractiveindex, wherein the third refractive index is different than the firstrefractive index and the second refractive index, wherein a portion oflight energy traveling via the waveguide radiates through the materiallayer to the optical detector.
 11. The interposer of claim 10 whereinthe detection layer is one of a polysilicon semiconductor layer and anamorphous semiconductor layer, the detection layer includes an n-dopedregion is disposed on a first end of the detection layer and a p-dopedregion is disposed on a second, opposite end of the detection layer. 12.The interposer of claim 11 wherein the detection layer includes a firstsurface, a first electrical contact connected to the first surface inthe p-doped region, a second electrical contact connected to the firstsurface in the n-doped region, and the waveguide is facing the firstsurface and is positioned to radiate energy on the first surface and isdisposed between the first and second electrical contacts.
 13. Theinterposer of claim 11 wherein the detection layer includes a firstsurface and a second surface that is opposite to the first surface, afirst electrical contact connected to the first surface in the p-dopedregion, a second electrical contact connected to the first surface inthe n-doped region, and the waveguide is facing the second surface andis positioned to radiate energy on the second surface.
 14. Theinterposer of claim 11 wherein the waveguide includes a first portionthat is adapted to radiate energy on a surface of the detection layer,the first portion includes at least one dimension that tapers towards aterminating end of the waveguide as the first portion extends to theterminating end in a direction that is substantially parallel to an axisthat extends through the p-doped region and is perpendicular to thedetection layer.
 15. The interposer of claim 10 wherein the waveguideincludes a first portion that radiates energy onto a surface of thedetection layer, the first portion includes at least one dimension thattapers to one end of a second portion that radiates energy onto thesurface of the detection layer and a third portion that extends from anopposite end of the second portion, the third portion radiates energyonto the surface of the detection layer and increases in size the atleast one dimension that was tapered in the tapered section.